This invention relates to an information processing apparatus connected to a network formed e.g., by a IEEE 1394 serial data bus, to an information processing method, and to a medium for having the information processing apparatus execute a program.
There has recently been developed AV (audio visual) equipment which allows for reciprocal information transmission over a network employing IEEE 1394 serial data buses standardized by the IEEE (The Institute of Electrical and Electronics Engineers). In this network system, the AV equipment, connected to the IEEE 1394 serial data buses, can be controlled reciprocally using a pre-set digital interface command (AV/C or command transaction set) referred to below as AV/C command. Each electronic device connected to the IEEE 1394 serial data buses is termed a unit, whilst the unit representing the function of each unit is termed a sub-unit. The information stored in each unit can be reciprocally read and written among the respective units using the descriptor prescribed in the general specifications of the AV/C command (AV/C digital interface command set general specification, referred to below as AV/C general).
The IEEE 1394 serial data buses are interconnected by bridges constituted by a set of electronic equipment, termed portals, such that data can be transmitted between two or more buses over the bridges. That is, although the number of devices (nodes) that can be connected to a sole IEEE 1394 serial data bus is limited to 63 at the maximum, more nodes can be connected by interconnecting plural buses over bridges to constitute a network made up of the buses and the bridges.
FIG. 1 shows an illustrative structure of a state in which the IEEE 1394 serial data buses are interconnected over the bridges.
In FIG. 1, nodes 101, 102 are connected to an IEEE 1394 serial data bus 103, whilst nodes 104 to 106 are connected to an IEEE 1394 serial data bus 107. In FIG. 1, the nodes 102, 104 serve as portals, these portals making up a bridge interconnecting the buses 103, 107. In the following, the nodes 102 and 104 are termed portals E and D, respectively. The nodes 101, 106 serve as controllers capable of reserving other equipment, whilst the node 105 is a target reserved by the controller. In the following, the nodes 101 and 106 are termed controllers A and B, respectively. It is assumed that, at this time point, the nodes ID(a), ID(b), ID(c), ID(d) and ID(e) are set in the controller A, controller B, target, portal D and in the portal E, respectively.
The flow in case the controller A reserves a target, and the controller B is searching for the reserve owner reserving the target, is shown in FIG. 2.
As a procedure P11, the controller A sends a reserve control command (RESERVE control command), prescribed as AV/C command, to the target (node 105), to reserve the target. The target reserved returns a response to the controller A while memorizing the node ID of the node which has reserved it (here, ID(a) of the controller A). The reserve control command and the response will be explained subsequently.
Next, as a procedure P12, the controller B sends a reserve status command (RESERVE status command), as later explained, to the target to inquire as to the identity of the reserve owner. This inquiry is made by searching a node ID of the reserve owner memorized by the target. Since the reserve owner at this time point is the controller A, the target notifies the controller B of node ID(a) of the controller A.
This enables the controller B to be apprized in a procedure P13 that the controller A is the reserve owner.
Meanwhile, if bus resetting has occurred on the IEEE 1394 serial data bus, topology re-setting occurs in the bus such that the node ID of each node connected to the bus is set to a new value.
However, the bus reset is not transmitted to outside the bridge, such that the information on the second setting of the node ID performed on a bus where the bus reset has occurred is not transmitted to outside the bridge.
That is, in the case of FIGS. 1 and 2, if a bus reset has occurred between the controller A and the bus 103, as the procedure P14, the node IDs of the controller A and the portal E connected to the bus 103 are updated. FIG. 1 shows a case in which, as a result of bus resetting, the controller A is changed from the node ID(a) to the node ID(f), whilst the portal E is changed from the node ID(e) to the node ID(g).
On the other hand, the controller B or the target of the other bus 107, connected over the bridge, are not aware of the fact that these node IDs have been secondarily set by the resetting of the bus 103.
Thus, if, after occurrence of bus resetting on the bus 103, the controller B makes an inquiry to the target as to the identity of its reserve owner, the latter supplies the controller B with the node ID(a) of the controller A prior to the occurrence of the bus resetting.
However, the node ID of the controller A at this time point has changed to the node ID(f), as described above, such that the controller B is unable to find that the reserve owner is the controller A.